CHEMISTRY, TOXICOLOGY, AND HUMAN HEALTH RISK OF CYANIDE COMPOUNDS IN SOILS AT FORMER MANUFACTURED-GAS PLANT SITES

Cyanide-containing wastes are commonly found in soils at former manufa ctured gas plant (MGP) sites, also known as town gas sites. The comple x forms of cyanide are responsible for the blue-stained soils and rock s found at these sites. Most concentrations of cyanide at MGP sites ar e below 2000 ppm, although concentrations greater than 20,000 ppm have been observed. An understanding of the chemistry of the MGP cyanide-c ontaining compounds, their fate, and transport as well as their toxico logy is critical to accurately assessing potential human health risks from these compounds. In this paper, the authors demonstrate that the most prevalent types of cyanide compounds found at former MGP sites ar e the relatively nontoxic iron-complexed forms, such as ferric ferrocy anide, rather than the highly toxic free cyanide forms. Moreover, the chemical conditions at most former MGP sites limit the extent to which free cyanide may be released into air and water from complex cyanides . Using a screening analysis, the authors estimate potential risks fro m a multiroute exposure to complex and free cyanides in soil, air, and groundwater at former MGP sites and demonstrate that such risks are l ikely to be insignificant. Unfortunately, the lack of readily availabl e measurement techniques to characterize cyanides in soil can result i n erroneous conclusions about potential risks from cyanide compounds i n soils at former MGP sites, particularly if health-based soil criteri a for free cyanide (e.g., the Massachusetts Department of Environmenta l Protection criterion for free cyanide is 100 ppm (MA. DEP, 1995)) ar e applied. The authors recommend development of routine methods for fi eld sampling and laboratory testing techniques to demonstrate that cya nides in soil at former MGP sites are predominated by iron-complexed s pecies and that free cyanide is less than levels of concern. (C) 1996 Academic Press, Inc.